21643020 has 144 divisors (see below), whose sum is σ = 76265280. Its totient is φ = 4866048.

The previous prime is 21643009. The next prime is 21643021. The reversal of 21643020 is 2034612.

It is a happy number.

21643020 is a `hidden beast` number, since 2 + 1 + 643 + 0 + 20 = 666.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21642984 and 21643002.

It is not an unprimeable number, because it can be changed into a prime (21643021) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 112044 + ... + 112236.

It is an arithmetic number, because the mean of its divisors is an integer number (529620).

Almost surely, 2^21643020 is an apocalyptic number.

21643020 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21643020, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38132640).

21643020 is an abundant number, since it is smaller than the sum of its proper divisors (54622260).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21643020 is a wasteful number, since it uses less digits than its factorization.

21643020 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 304 (or 299 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 18.

The square root of 21643020 is about 4652.2059283742. The cubic root of 21643020 is about 278.6800973612.

Adding to 21643020 its reverse (2034612), we get a palindrome (23677632).

It can be divided in two parts, 2164 and 3020, that added together give a square (5184 = 72²).

The spelling of 21643020 in words is "twenty-one million, six hundred forty-three thousand, twenty".